Have a really nice 2003 Silverado Ext Cab LT Z71. 5.7 litres. It's been well maintained, 156,000 miles. Using a small amount of engine coolant about every 4 to 5 months. Still runs good, plenty of power, no smoke that I see. Wandering what the most common culprit is here. Thanks.

 

Welcome to the forum from Florida. A very small leak every 4 or 5 months is not very much. This is so small that you won't even notice it under the truck. It could be from many places and I would just keep an eye on it for now.

 

the only options are external leak or internal leak
external leaks can be found by pressure testing the system with a cooling system pressure tester...common leak sources would be water pump and intake manifold gaskets. I have seen a few weak lower rad hose spring clamps allow fluid seepage.

internal leaks are less common they enter the cylinder or crank case or transmission.